Opswat gauges usage by looking at the software installed on computers running their AppRemover program. The data came from more than 150,000 computers.

When asked about the differences between Opswat's numbers and research and analysis firm NPD, Opswat marketing manager Elisse Lockhart wrote in an e-mail, "Our data looks at all applications installed on machines and aggregates various versions of products, so that can include people who are using very old applications. I believe NPD's report only looks at new sales, so they would capture more of the upcoming products than the software that people already have installed."

Related stories:

Although the report is imperfect, it does provide a snapshot of the security software running on a large number of Windows computers. While Avast remains on top of the global vendor list, with their free suite and two paid upgrades, they've been bumped to second place in single-product comparisons between MSE and Avast Antivirus Free.

MSE took the most popular product lead with 15.3 percent market share, followed by Avast at 13.6 percent, free Avira at 9 percent, ESET's NOD32 at 6.8 percent, and free AVG at 6.2 percent. NOD32 was the only paid program in the top five globally.

In North America, MSE gained 9.1 percent market share to land at 30.4 percent -- nearly one-third of the entire market. Avast Free came in at 8.4 percent, while AVG landed third at 7 percent, a loss of 0.7 percent from the market. Norton Internet Security and Norton AntiVirus are the first paid products on the North American chart, coming in at 4th and 5th with 4.7 percent and 4.5 percent, respectively.

Another interesting statistic that Opswat noted was how recently a security suite has updated its virus definition files. While MSE led the pack with more than 94 percent of people running it having also received an update, that doesn't necessarily track with how secure a program is. MSE recently failed AV-Test's certification.

Time since last update in top security suites.

(Credit:
Opswat)

Opswat also provided some initial operating system stats, with
Windows 7 usage still on the rise, Windows XP on the decline, and
Windows 8 barely leaving a mark. Worldwide, Opswat found Windows 7 on 53.8 percent of computers, an increase of 4 percent. XP fell 6.6 percent globally to 36.2 percent, and fell in the North American market 5.3 percent to 37 percent. Windows 7 rose in North America just under 3 percent to 48.3 percent.

As a point of comparison, Opswat's Windows market share numbers track were hit and miss with the better-known NetMarketShare. NetMarketShare placed Windows 7 at 51.62 percent in North America and 44.71 percent worldwide, and Windows XP at 21.19 percent in North America and 39.82 percent globally.

Opswat's stats on global Windows operating system usage.

(Credit:
Opswat)

Not surprisingly, Windows 8, which was only released three weeks before the data in the report was compiled, accounts for less than one percent of the market on both.

We can see from these numbers that even with bad test scores, Microsoft Security Essentials remains a growing force in computer protection. It will be interesting to see what happens to security suite numbers as Windows 8 becomes more widely used. Will people continue to use security software as they have? Or will the touch-and-mobile Windows 8 force a shake-up in personal computer security, too?

Senior writer Seth Rosenblatt covers Google and security for CNET News, with occasional forays into tech and pop culture. Formerly a CNET Reviews senior editor for software, he has written about nearly every category of software and app available.